The present invention relates generally to measuring the impedance value of passive electronic components, and in particular to measuring capacitance using a charge measuring system.
Many of the well-known methods and circuits for measuring various properties of capacitors, including capacitance, leakage, parallel resistance, etc., are complex, difficult to perform or operate, subject to interpretation, and expensive. These include capacitance bridges, operational amplifiers, and other precision instrumentation. Often such equipment is found only in well-equipped repair and calibration shops.
It is well recognized that it would be desirable to include a capacitance measurement feature in an ordinary multimeter such as may be used in servicing electrical equipment. Such multimeters, generally designed to measure voltage, current, and D.C. resistance, are typically small, lightweight, and relatively inexpensive, and, accordingly, are very popular among service technicians in general. While rough capacitance estimates can often be made by observing the approximate charging time of an unkown capacitor through the resistance measuring circuit of a multimeter, most multimeter users would prefer a more accurate, but still minimal cost, method of measuring capacitance. However, the addition of known capacitance measuring systems, such as the complex signal conditioning systems mentioned above, add significant costs and bulk beyond those contemplated for basic multimeters. Also, for use in multimeters, the accidental misapplication of voltage to a capacitance measuring circuit must be anticipated. Series-connected impedances which prevent circuit damage may be impractical due to the difficulty of isolating true capacitance from the error-inducing effects of added impedances.